feat: named server sets — save/apply the Active/Disabled split (#52)

Sets live in the config under _bccServerSets (bcc-owned, ignored by
Claude, travels with the file). Apply enables exactly the set's members
and parks the rest; vanished members are reported, not fatal. GUI row:
set combo + Apply + Save set… + delete.

Closes #52

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bcc_core.py

@@ -39,6 +39,12 @@ CONFIG_FILENAME = "claude_desktop_config.json"
 # we can toggle it back on without losing the definition.
 DISABLED_KEY = "_disabledMcpServers"
 
+# Named server sets: {set_name: [enabled server names]}. Same pattern as
+# DISABLED_KEY — a bcc-owned key Claude ignores, stored in the config file so
+# sets travel with it. Applying a set enables exactly the listed servers and
+# parks the rest under DISABLED_KEY.
+SETS_KEY = "_bccServerSets"
+
 BACKUP_DIRNAME = ".bcc_backups"
 MAX_BACKUPS = 15
 
@@ -409,6 +415,70 @@ def extract_servers(cfg: dict) -> list[ServerEntry]:
     return out
 
 
+# --------------------------------------------------------------------------- #
+# Named server sets (issue #52)
+# --------------------------------------------------------------------------- #
+def list_server_sets(cfg: dict) -> dict[str, list[str]]:
+    """
+    Return {set_name: [enabled server names]} from cfg's SETS_KEY.
+
+    Fail-soft: entries whose value isn't a list of strings (hand-edited or
+    corrupted) are skipped rather than raising, so one bad set never hides
+    the rest.
+    """
+    raw = cfg.get(SETS_KEY)
+    if not isinstance(raw, dict):
+        return {}
+    out: dict[str, list[str]] = {}
+    for name, members in raw.items():
+        if isinstance(members, list) and all(isinstance(m, str) for m in members):
+            out[str(name)] = list(members)
+    return out
+
+
+def save_server_set(cfg: dict, name: str, servers: list[ServerEntry]) -> list[str]:
+    """
+    Snapshot the current enabled-server names into cfg under SETS_KEY as
+    `name` (overwriting an existing set of that name). Returns the saved
+    member list. The caller decides when cfg reaches disk (normal Save flow).
+    """
+    members = [s.name for s in servers if s.enabled]
+    sets = cfg.get(SETS_KEY)
+    if not isinstance(sets, dict):
+        sets = {}
+        cfg[SETS_KEY] = sets
+    sets[name] = members
+    return members
+
+
+def delete_server_set(cfg: dict, name: str) -> bool:
+    """Remove set `name` from cfg. Drops SETS_KEY entirely when the last set
+    goes, so untouched configs don't grow an empty bcc key. Returns True if
+    something was deleted."""
+    sets = cfg.get(SETS_KEY)
+    if not isinstance(sets, dict) or name not in sets:
+        return False
+    del sets[name]
+    if not sets:
+        cfg.pop(SETS_KEY, None)
+    return True
+
+
+def apply_server_set(servers: list[ServerEntry], enabled_names: list[str]) -> list[str]:
+    """
+    Enable exactly the servers named in `enabled_names`; disable every other
+    entry (in place). Returns the set members that no longer exist in
+    `servers` — the caller surfaces those as a warning, and the rest of the
+    set still applies.
+    """
+    wanted = set(enabled_names)
+    present: set[str] = set()
+    for s in servers:
+        s.enabled = s.name in wanted
+        present.add(s.name)
+    return sorted(wanted - present)
+
+
 def resolve_name_collision(name: str, existing: set[str]) -> str:
     """
     Return a name guaranteed not to collide with `existing`.